The present invention relates to a driver circuit for wide gap semiconductor switching device made of SiC, GaN or the like.
As for the wide gap semiconductor switching devices, silicon carbide (SiC), gallium nitride (GaN) or the like is drawing the attention. These materials have a dielectric breakdown voltage strength that is approximately ten times as high as that of Si, and a drift layer for ensuring the withstand voltage can be made thin to approximately one tenth. Therefore, it is possible to implement a lower on-voltage of power devices. Even in a high withstand voltage region in which only bipolar devices can be used with Si, therefore, it becomes possible to use unipolar devices in wide gap semiconductor devices made of SiC or the like. In Si-IGBTs which form the main stream of power devices at the present time, there is a built-in voltage of approximately 1 V. In MOSFETs and junction-type FETs (abbreviated to JFETs) which are unipolar devices made of SiC, however, devices having no built-in voltage can be obtained.
In addition, a SiC substrate indicates a high thermal conductivity and it is a power device that can operate at high temperatures as well. However, it is known that the dependence of the on-resistance upon the temperature is large in unipolar devices. FIG. 2 shows relations between the junction temperature and the mounting area under different cases of the dependence upon the temperature. The loss in a SiC power semiconductor device is set equal to half of that of Si (when Tj=137° C.). A dashed line in FIG. 2 indicates a mounting area ratio in the case where the loss in the power semiconductor device has no dependence upon the temperature. A solid line in FIG. 2 indicates a mounting area ratio in the case where the loss in the power semiconductor device increases in proportion to the 2.4th power of the temperature. If the power semiconductor device having a loss that does not depend upon the temperature is used at a junction temperature of at least 200° C., the mounting area of the power semiconductor device can be made half or less. On the other hand, if the power semiconductor device having a loss that increases in proportion to the 2.4th power of the temperature is used at a junction temperature of at least 200° C., the mounting area of the power semiconductor device must be made at least 60%. Therefore, a control method of detecting the temperature of the power semiconductor device and lowering the dependence of the loss upon the temperature is important.
As for the technique for detecting the temperature of the semiconductor device, a method using a thermistor and a method using a measurement result of the on-voltage of a temperature detecting diode formed in a Si-IGBT are known as methods typically used in intelligent power modules and so on are well known. The method using the temperature detecting diode is disclosed in JP-A-10-38964.